1. Field of the Invention
The present invention concerns a rapidly expanding metallic mixture comprising a metal salt and a metal powder, which is treated to prevent oxidation thereof at room temperature and which thus prevents spontaneous explosion thereof due to oxidation of the metal powder at room temperature during storage, or dysfunction of the mixture upon blasting work because of improper mixing ratios between the metal salt and the metal powder.
2. Description of the Prior Art
The rapidly expanding metallic mixture was invented by the present inventors, and was patented by the Korean Intellectual Property Office (Korean Patent No. 10-0213577).
The rapidly expanding metallic mixture disclosed in Korean Patent No. 10-0213577 can be defined as follows.
In a mixture comprising a metal salt and a metal powder subjected to a high temperature of 700° C. or more (as such, the temperature to be applied varies with types and mixing ratios of the metal salt and the metal powder), while the metal salt oxidizes the metal powder, oxidation heat of ultrahigh temperatures (3,000-30,000° C.) is instantaneously created. When such a reaction is induced in a closed space, superhigh pressure of vapor expansion (40,000-60,000 kg/cm2) is generated due to the oxidation heat. Immediately after such expansion, the reaction products shrink in volume. The present inventors confirmed the reaction results through repeated experiments involving the above reaction. In particular, the above reaction readily proceeds upon mixing of the metal salt and the light metal powder having relatively low melting points.
In this regard, when a mixture of ferrous nitrate (Fe(NO3)2) and manganese (Mn) powder is subjected to a thermal shock of about 1500° C., the following reaction occurs.2Fe(NO3)3+12Mn→2FeO+4Mn3O4+3N2
In the above reaction, oxidation heat of 10,000° C. or higher is created, by which iron (Fe) and manganese oxide (Mn3O4) products are vaporized and rapidly expanded. During vaporization and rapid expansion, a reverse reaction of the above reaction does not occur. When the volume of the reaction products increases larger by rapid expansion, internal temperature decreases. As such, iron (Fe) and manganese oxide (Mn3O4) are changed from gaseous state to solid state, and expansion pressure disappears instantaneously. A phenomenon of temperature decrease due to rapid expansion can be explained according to a Charles' Law related to volume and temperature, or the theory of adiabatic expansion.
Thus, the rapidly expanding metallic mixture is defined as a mixture comprising the metal salt acting as an oxidizing agent and the metal powder oxidized at high temperatures of 700° C. or more by the metal salt.
Upon oxidation, oxidation heat which is ultrahigh temperature heat of 3,000-30,000° C. is generated, by which vaporization and expansion of the reaction products occur, thus creating superhigh pressure of 40,000-60,000 kg/cm2 in the closed space.
Such oxidation reaction and rapid expansion occurring only at high temperature conditions suggest industrial applicability of the metallic mixture. Hence, the metallic mixture can be substituted for conventionally used dynamite, thus being suitable for use in blasting rock masses in construction works. Compared to dynamite, the metallic mixture of the present invention is much higher in expansion force and shorter in a time period required for oxidation. In addition, immediately after the condition of high temperature is removed by rapid expansion, the vaporization-expanded product is changed to solid state and thus expansion reaction stops. Therefore, there is no scattering of the broken rock fragments, and explosive sound during rapid expansion is remarkably reduced. The reason why conventional gunpowder and the inventive metallic mixture have different effects is that conventional gunpowder employs oxidation and vaporization of organic materials, whereas the rapidly expanding metallic mixture of the present invention uses oxidation and vaporization of metals. In such conventional gunpowder, even though the internal temperature is decreased after rapid expansion, gas products are not changed again to solid state, but are diffused in gaseous state. So, conventional gunpowder suffers from the disadvantages in terms of scattering many fragments, and creating a loud explosive sound and large explosive vibration. Further, since typically used gunpowder may be ignited even at relatively low temperatures of about 250° C., it should be carefully handled during transport and storage. However, the inventive metallic mixture is advantageous in light of no possibility of accidental explosion during storage and handling of such materials due to the oxidation reaction being generated only at high temperatures which are not easily applied.
A mixing ratio of the metal salt and the metal powder is defined as a ratio of an oxygen amount generated from the metal salt and an oxygen amount required for oxidization of the metal powder, which is a ratio of molecular weights calculated from chemical formulas. The time period required for oxidation of the metal powder in a single capsule is a moment in the range of {fraction (1/2,000)} to {fraction (1/100)} sec.
The mixture of the metal salt and the metal powder is formulated in the form of a capsule and stored at room temperature. Even though the mixture is stored in a sealed state, the metal powder may be exposed to moisture or air by penetrating moisture or air into the mixture through connection of triggering devices. In such case, oxidation of the metal powder proceeds, which causes the following problems.
First, the rapidly expanding metallic mixture is not accidentally exploded by external impetus or impacts, but there is a possibility of triggering high temperature oxidation of the metallic mixture itself by oxidation heat created when the metal powder in the mixture is oxidized by moisture or air at room temperature. This is understood by the phenomenon of explosion of light metals such as magnesium upon contact with water at room temperature, with generating very high oxidation heat.
Second, during oxidation, an initial mixing ratio of the metal salt versus the metal powder is changed, and the oxidation reaction is not triggered at an expected oxidation temperature, or the desired rapid expansion force cannot be obtained even though the oxidation reaction occurs.